1. Field of the Invention
The present invention relates to subterranean cementing operations, and more particularly, to cement compositions comprising strength-enhancing lost circulation materials, and methods of using such cementing compositions in subterranean formations.
2. Description of the Related Art
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Subterranean formations transversed by well bores are often weak, highly permeable, and extensively fractured. In some cases, such formations may be unable to withstand the hydrostatic head pressure normally associated with fluids (e.g., cement compositions and the like) being injected into the formation. In such cases, the hydrostatic pressure may be sufficient to force such fluids into the fractures and/or permeable zones of the formation, which may result in a significant loss of fluid into the formation. This loss of fluid circulation is problematic for a number of reasons. For example, where the loss of circulation occurs during a cementing operation, excessive fluid loss may cause a cement composition to be prematurely dehydrated and may decrease the compressive strength of the cement composition. Excessive fluid loss into the formation may also prevent or reduce bond strength between the set cement composition and the subterranean zone, the walls of pipe, and/or the walls of the well bore.
Previous attempts to minimize the loss of circulation into the subterranean formation involved the addition to the cement composition of a variety of additives including, but not limited to, asphaltines, ground coal, cellulosic, plastic materials, and the like. The addition of such additives was an attempt to plug or bridge the fractures and/or the permeable zones in the formation where the treatment fluids are typically lost. However, during a cementing operation, the addition of the lost circulation materials often has been detrimental to the compressive strength of the cement composition because, inter alia, such additives do not bond to the cement. Because one function of the cement is to support the pipe string in the well bore, such reduction in the compressive strength of the cement composition is undesirable.